Power-up signal generation circuit

ABSTRACT

A power-up signal generation circuit includes a control signal generation unit suitable for generating first and second control voltages based on a power-up signal, a level tracing voltage generation unit suitable for generating a level tracing voltage whose voltage level varies based on the first and second control voltages, and a power-up signal generation unit suitable for generating the power-up signal based on the level tracing voltage, and providing a feedback on the power-up signal to the control signal generation unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of Korean Patent Application No.10-2014-0021933, filed on Feb. 25, 2014, which is incorporated herein byreference in its entirety.

BACKGROUND

1. Field

Various embodiments of the present invention relate to semiconductordesign technology, and more particularly, to a power-up signalgeneration circuit in a semiconductor device.

2. Description of the Related Art

Semiconductor devices, such as a dynamic random access memory (DRAM),generally include a power-up signal generation circuit to secure astable operation of an internal circuit. When an external power voltageVDD is supplied to a semiconductor device, the external power voltageVDD gradually increases to a target level.

However, if the external power voltage VDD is directly supplied to theinternal circuit of the semiconductor device before the external powervoltage VDD reaches the target level a latch-up phenomenon may occur.Thus, the semiconductor device may be damaged. To prevent suchphenomenon from occurring, a power-up signal generation circuit isincluded in the semiconductor device. The power-up signal generationcircuit activates a power-up signal when the external power voltage VDDreaches the target level to stably operate the internal circuit andinitialize the semiconductor device.

FIG. 1 is a circuit diagram illustrating a conventional power-up signalgeneration circuit, and FIG. 2 shows timing diagrams of an externalpower voltage VDD and a power-up signal PWRUP in the power-up signalgeneration circuit shown in FIG. 1.

Referring to FIG. 1, the external power voltage VDD supplied to thepower-up signal generation circuit is divided by resistors R11 and R12,and the divided voltage is outputted as a level tracing voltage V_LEVEL.The level tracing voltage V_LEVEL has a voltage level that linearlyvaries according to a level of the external power voltage VDD.

An NMOS transistor N11 receives the level tracing voltage V_LEVELthrough a gate thereof and is turned on more strongly as the level ofthe external power voltage VDD becomes higher. As the NMOS transistorN11 is turned on more strongly, a detection voltage V_DET becomes lowergradually. When the detection voltage V_DET is lower than a certainlevel, that is, when the external power voltage VDD becomes higher thana target voltage V_TARGET, the power-up signal PWRUP is activated to alogic high level by an inverter.

Referring to FIG. 2, a variation of the power-up signal PWRUP based onvariation of the external power voltage VDD is described herein, alongwith the concerns of the conventional technology for the power-up signalPWRUP.

In a duration prior to a time “t1” the external power voltage VDD, whichis applied to a circuit to turn on the power of a semiconductor device,is gradually increased. However, since the external power voltage VDDhas not yet reached the target voltage V_TARGET, the power-up signalPWRUP is in a deactivated state of a logic low level.

In a duration between the time “t1” and a time “t2”, the external powervoltage VDD is increased higher than the target voltage V_TARGET. TheNMOS transistor N11 is strongly turned on to enable the power-up signalPWRUP to a logic high level.

In a duration between the time “t2” and a time “t3”, the currentconsumption amount of the semiconductor device is increased and theexternal power voltage VDD drops. For example, such a voltage drop mayoccur when a DRAM device performs an active operation “ACT”. When theexternal power voltage VDD drops lower than the target voltage V_TARGET,the detection voltage V_DET may be raised. When the detection voltageV_DET is raised and then drops, the power-up signal PWRUP is reset“RESET” and as a result the semiconductor device in the middle of anoperation may be inadvertently initialized again.

SUMMARY

Various embodiments of the present invention are directed to a power-upsignal generation circuit: of a semiconductor device capable of stablyoperating by generating a power-up signal in a state in which a voltagelevel of an external power voltage sufficiently rises by adjusting alevel tracing voltage and increasing a voltage level of a target voltagebefore a power-up.

Various embodiments of the present invention are directed to a power-upsignal generation circuit of a semiconductor device capable ofpreventing an initialization of an operating semiconductor device byadjusting a level tracing voltage and decreasing a voltage level of atarget voltage after a power-up.

In accordance with an embodiment of the present invention, a power-upsignal generation circuit may include: a control signal generation unitsuitable for generating first and second control voltages based on apower-up signal; a level tracing voltage generation unit suitable forgenerating a level tracing voltage whose voltage level varies based onthe first and second control voltages; and a power-up signal generationunit suitable for generating the power-up signal based on the leveltracing voltage, and providing a feedback on the power-up signal to thecontrol signal generation unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating a conventional power-up signalgeneration circuit.

FIG. 2 is a timing diagram of a power-up signal generation circuit shownin FIG. 1.

FIG. 3 is a diagram illustrating a power-up signal generation circuit inaccordance with an embodiment of the present invention.

FIG. 4 is a detailed diagram of a control signal generation unit shownin FIG. 3.

FIG. 5 is a graph illustrating a resistance characteristic of a variableresistor according to a control voltage.

FIG. 6 is a table showing parameters for describing an operation of thepower-up signal generation circuit shown in FIG. 3.

FIG. 7 is a waveform diagram showing voltages varying before and after apower-up in the power-up signal generation circuit shown in FIG. 3.

FIG. 8 is a diagram illustrating a power-up signal generation circuit inaccordance with an embodiment of the present invention.

FIG. 9 is a detailed diagram of a control signal generation unit shownin FIG. 8.

FIG. 10 is a table showing parameters for describing an operation of thepower-up signal generation circuit shown in FIG. 8.

FIG. 11 is a waveform diagram illustrating a voltage varying before andafter a power-up in the power-up signal generation circuit shown in FIG.8.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstrued as limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. The drawings are not necessarily to scale andin some instances, proportions may have been exaggerated to clearlyillustrate features of the embodiments. Throughout the disclosure,reference numerals correspond directly to the like numbered parts in thevarious figures and embodiments of the present invention. It is alsonoted that in this specification, “connected/coupled” refers to onecomponent not only directly coupling another component but alsoindirectly coupling another component through an intermediate component.In addition, a singular form may include a plural form as long as it isnot specifically mentioned in a sentence.

FIG. 3 is a diagram illustrating a power-up signal generation circuit inaccordance with an embodiment of the present invention.

Referring to FIG. 3, the power-up signal generation circuit may includea control signal generation unit 100, a level tracing voltage generationunit 200A and a power-up signal generation unit 400.

The control signal generation unit 100 generates first and secondcontrol voltages VCTRL1 and VCTRL2 based on a power-up signal PWRUP. Thecontrol signal generation unit 100 performs an initialization operation.That is, before a power-up the control signal generation unit 100outputs a ground voltage VSS as the first control voltage VCTRL1 andoutputs a supply voltage VDD as the second control voltage VCTRL2.Further, after the power-up, the control signal generation unit 100inverts and outputs voltage levels of the first and second controlvoltages VCTRL1 and VCTRL2 at its output node whenever the power-upsignal PWRUP toggles from a logic low level to a logic high level.

Here, “before the power-up” means a duration in which the power-upsignal PWRUP is deactivated to a logic low level, and “after thepower-up” means a duration in which the power-up signal PWRUP isactivated to a logic high level.

The level tracing voltage generation unit 200A generates a level tracingvoltage V_LEVEL by dividing the supply voltage VDD based on the firstand second control voltages VCTRL1 and VCTRL2. The level tracing voltagegeneration unit 200A may include first and second variable resistors R1and R2 coupled in series between a supply voltage (VDD) terminal and aground voltage (VSS) terminal.

The level tracing voltage V_LEVEL controls a target voltage V_TARGET fordetermining an activation timing of the power-up signal PWRUP.

Before the power-up, the power-up signal PWRUP is controlled to beactivated after the supply voltage VDD becomes higher than the targetvoltage V_TARGET. Before the power-up, the target voltage V_TARGET maybe set relatively high to activate the power-up signal PWRUP relativelylater. After the power-up, the target voltage V_TARGET may be setrelatively low so that a reset of the power-up signal PWRUP rarelyoccurs. In the embodiment of the present invention, the level tracingvoltage generation unit 200A controls the level tracing voltage V_LEVEL.That is, the level tracing voltage generation unit 200A outputs thelevel tracing voltage V_LEVEL having a relatively low voltage level at afirst node ND1 before the power-up, and outputs the level tracingvoltage V_LEVEL having a relatively high voltage level at the first nodeND1 after the power-up.

The power-up signal generation unit 400 generates the power-up signalPWRUP based on the level tracing voltage V_LEVEL. A feedback on thepower-up signal PWRUP generated from the power-up signal generation unit400 is given to the control signal generation unit 100.

The power-up signal generation unit 400 may include a detection voltagegeneration section 400A and a power-up signal output section 400B. Thedetection voltage generation section 400A generates a detection voltageV_DET with a voltage level controlled based on the level tracing voltageV_LEVEL. The power-up signal output section 4006 outputs the power-upsignal PWRUP based on the detection voltage V_DET.

The detection voltage generation section 400A includes a PMOS transistorP1 and a NMOS transistor N1 coupled in series between the supply voltage(VDD) terminal and the ground voltage (VSS) terminal. The PMOStransistor P1 is coupled between the supply voltage (VDD) terminal and asecond node ND2, and has a gate receiving the ground voltage VSS. Sincethe PMOS transistor P1 is turned on by the ground voltage VSS applied toits gate, an initial voltage level of the second node ND2 maintains asupply voltage (VDD) level. The NMOS transistor N1 is coupled betweenthe second node ND2 and the ground voltage (VSS) terminal, and has agate receiving the level tracing voltage V_LEVEL. The detection voltageV_DET is outputted through the second node ND2. Since the extent of theturn-on of the NMOS transistor N1 is determined based on the leveltracing voltage V_LEVEL applied to its gate, the detection voltage V_DETmay have a voltage level controlled by the level tracing voltageV_LEVEL.

The power-up signal output section 400B may change a logic level of thepower-up signal PWRUP when the detection voltage V_DET has a levelhigher that a logic threshold value of an inverter.

FIG. 4 is a detailed diagram of the control signal generation unit 100shown in FIG. 3.

Referring to FIG. 4, the control signal generation unit 100 may includea first edge-triggered flip-flop 110A, a second edge-triggered flip-flop110B and an initialization section 120.

The first and second edge-triggered flip-flops 110A and 1108 generatethe first and second control voltages VCTRL1 and VCTRL2, respectively,based on the power-up signal PWRUP. The first and second edge-triggeredflip-flops 110A and 110B are disabled before the power-up, and invertand output the voltage levels of the first and second control voltagesVCTRL1 and VCTRL2, respectively, whenever the power-up signal PWRUPtoggles from a logic low level to a logic high level.

The first edge-triggered flip-flop 110A may include arising-edge-triggered flip-flop which inverts and outputs the voltagelevel of the first control voltage VCTRL1 at its output terminal Qwhenever the power-up signal PWRUP toggles from a logic low level to alogic high level. That is, the ground voltage VSS is inputted to thefirst edge-triggered flip-flop 110A through its data input terminal D,and the power-up signal PWRUP is inputted to the first edge-triggeredflip-flop 110A through its clock terminal CLK. The second edge-triggeredflip-flop 1108 may include a rising-edge-triggered flip-flop whichinverts and outputs the voltage level of the second control voltageVCTRL2 at its output terminal Q whenever the power-up signal PWRUPtoggles from a logic low level to a logic high level. That is, thesupply voltage VDD is inputted to the second edge-triggered flip-flop1108 through its data input terminal D, and the power-up signal PWRUP isinputted to the second edge-triggered flip-flop 1108 through its clockterminal CLK.

The initialization section 120 initializes the first control voltageVCTRL1 to the ground voltage VSS and the second control voltage VCTRL2to the supply voltage VDD before the power-up, that is, before thepower-up signal PWRUP reaches a given voltage level. The initializationsection 120 includes a PMOS transistor P2 and an NMOS transistor N2. ThePMOS transistor P2 is coupled between the supply voltage (VDD) terminaland the output node of the second edge-triggered flip-flop 110B, and hasa gate receiving the power-up signal PWRUP. The NMOS transistor N2 iscoupled between the output node of the first edge-triggered flip-flop110A and the ground voltage (VSS) terminal, and has a gate receiving aninverted signal of the power-up signal PWRUP through an inverter IV1.

Accordingly, the PMOS transistor P2 and the NMOS transistor N2 of theinitialization section 120 are turned on to initialize the first controlvoltage VCTRL1 to the ground voltage VSS and the second control voltageVCTRL2 to the supply voltage VDD before the power-up, respectively. ThePMOS transistor P2 and the NMOS transistor N2 are turned off after thepower-up.

FIG. 5 is a graph showing a resistance characteristic of a variableresistor according to a control voltage.

Referring to FIG. 5, a variable resistor “A” has a positive coefficientto the control voltage that is a directly proportional relationship. Theresistance of the variable resistor “A” increases as a voltage level ofthe control voltage changes into a second level VCTRL2 from a firstlevel VCTRL1. A variable resistor “B” has a negative coefficient to thecontrol voltage, that is, an inversely proportional relationship. Theresistance of the variable resistor “B′” decreases as the voltage levelof the control voltage changes into the second level VCTRL2 from thefirst level VCTRL1.

In the embodiment of the present invention, the first and secondvariable resistors R1 and R2 provided in the level tracing voltagegeneration unit 200A may be the variable resistor “B” which has thenegative coefficient to the control voltage, that is, an inverselyproportional relationship. However, the present invention is not limitedto this structure, and the first and second variable resistors R1 and R2may be the variable resistor “A” which has the positive coefficient tothe control voltage, that is, a directly proportional relationship).

Hereinafter, an operation of the power-up signal generation circuit ofFIG. 3 will be described with reference to FIGS. 3, 4, 6 and 7.

FIG. 6 is a table showing parameters for describing an operation of thepower-up signal generation circuit of FIG. 3, such as VCTRL1, VCTRL2,R1, R2, V_LEVEL and V_TARGET. FIG. 7 is a waveform diagram showingvoltages varying before and after the power-up in the power-up signalgeneration circuit shown in FIG. 3.

Referring to FIGS. 3 and 6, before the power-up, the resistance of thefirst variable resistor R1 is controlled to have a minimum value R1(min)in response to the first control voltage VCTRL1 having a ground voltage(VSS) level, and the resistance of the second variable resistor R2 iscontrolled to have a value [R2(min)−{R2(delta)*VDDH}] smaller than theresistance of the first variable resistor R1, in response to the secondcontrol voltage VCTRL2 having a supply voltage (VDD) level.

As the resistance of the second variable resistor R2 is smaller than theresistance of the first variable resistor R1 before the power-up, thelevel tracing voltage V_LEVEL at the first node ND1, which is set to{1−R1/(R1+R2)}*VDD, becomes lower. Since the NMOS transistor N1 isweakly turned on based on the level tracing voltage V_LEVEL becominglower, the voltage level of the detection voltage V_DET at the secondnode ND2 becomes higher. Accordingly, the power-up signal PWRUP isdeactivated to a logic low level in response to the voltage level of thedetection voltage V_DET becoming higher.

That is, referring to FIG. 7, before the power-up, the level tracingvoltage V_LEVEL having a lower voltage level is outputted at the firstnode ND1 so that the power-up signal PWRUP is activated after the supplyvoltage VDD becomes higher than the target voltage V_TARGET.Accordingly, the power-up timing when the supply voltage VDD reaches thevoltage level of the target voltage V_TARGET may be adjusted. After thepower-up, the resistance of the first variable resistor R1 is controlledto have a minimum value [R1(min)−{R1(delta)*VDD}] in response to thefirst control voltage VCTRL1 having the supply voltage (VDD) level, andthe resistance of the second variable resistor R2 is controlled to havea value R2(min) greater than the resistance of the first variableresistor R1, in response to the second control voltage VCTRL2 having theground voltage (VSS) level.

As the resistance of the second variable resistor R2 is greater than theresistance of the first variable resistor R1 after the power-up, thelevel tracing voltage V_LEVEL at the first node ND1, which is set to{1−R1/(R1+R2)}*VDD, becomes higher. Since the NMOS transistor N1 isstrongly turned on in response to the level tracing voltage V_LEVELbecoming higher, the voltage level of the detection voltage V_DET at thesecond node ND2 becomes lower. Accordingly, the power-up signal PWRUP isactivated to a logic high level in response to the voltage level of thedetection voltage V_DET becoming lower.

That is, referring to FIG. 7, after the power-up, the level tracingvoltage V_LEVEL having a higher voltage level is outputted through thefirst node ND1 to control the target voltage V_TARGET to be lower, sothat a reset of the power-up signal PWRUP rarely occurs.

FIG. 8 is a diagram illustrating a power-up signal generation circuit inaccordance with an embodiment of the present invention.

Referring to FIG. 8, the power-up signal generation circuit may includethe control signal generation unit 100, a level tracing voltagegeneration unit 200B and the power-up signal generation unit 400.

The level tracing voltage generation unit 200B may include a voltagedivider having the first and second variable resistors R1 and R2 of FIG.3 and a compensation section. The compensation section may include a NMStransistor N3.

The control signal generation unit 100 generates first and secondcontrol voltages VCTRL1 and VCTRL2 in response to a power-up signalPWRUPB. The control signal generation unit 100 performs aninitialization operation. That is, the control signal generation unit100 outputs a supply voltage VDD as the first control voltage VCTRL1 andoutputs a ground voltage VSS as the second control voltage VCTRL2 beforea power-up. Further, after the power-up, the control signal generationunit 100 inverts and outputs voltage levels of the first and secondcontrol voltages VCTRL1 and VCTRL2 at its output node whenever thepower-up signal PWRUPB toggles to a logic low level from a logic highlevel.

Here, “before the power-up” means a duration in which the power-upsignal PWRUPB is deactivated to a level corresponding to the supplyvoltage VDD, and “after the power-up” means a duration that the power-upsignal PWRUPB is activated to a logic low level.

The level tracing voltage generation unit 200B generates a level tracingvoltage V_LEVEL by dividing the supply voltage VDD and the groundvoltage VSS in response to the first and second control voltages VCTRL1and VCTRL2. The level tracing voltage generation unit 200B may includefirst and second variable resistors R1 and R2 coupled between a supplyvoltage (VDD) terminal and a ground voltage (VSS) terminal in series.

The level tracing voltage generation unit 200B in accordance with theembodiment of the present invention may further include the compensationsection that compensates for the level tracing voltage V_LEVEL changingaccording to the environment condition. The environment condition mayvary according to process, voltage and temperature (PVT).

The compensation section may include the NMOS transistor N3 which servesas a current source. The NMOS transistor N3 is coupled between thesecond variable resistor R2 and the ground voltage (VSS) terminal, andhas a gate receiving an enable signal V_EN, which is outputted at athird node ND3 between the first variable resistor R1 and the secondvariable resistor R2. The extent of the turn-on of the NMOS transistorN3 is controlled in response to a voltage level V_EN of the third nodeND3. When the voltage level V_EN of the third node ND3 is lower than athreshold voltage (Vth) of the NMOS transistor N3, no current flowsthrough the NMOS transistor N3. When the threshold voltage (Vth) of theNMOS transistor N3 becomes lower, the voltage level V_EN of the thirdnode ND3 becomes lower and the NMOS transistor N3 compensates thevoltage level V_EN of the third node ND3. That is, the NMOS transistorN3 compensates a process variation. When the threshold voltage (Vth) ofthe NMOS transistor N3 becomes lower, a current flowing in the first andsecond variable resistors R1 and R2 is greater, so that the voltagelevel of the enable signal V_EN is lower.

The level tracing voltage V_LEVEL is used to control a target voltageV_TARGET for determining an activation timing of the power-up signalPWRUPB.

In the embodiment of the present invention, before the power-up, thepower-up signal PWRUPB may be activated to a logic low level after thesupply voltage VDD becomes higher than the target voltage V_TARGET.Before the power-up, the target voltage V_TARGET may be set relativelyhigh so as to activate the power-up signal PWRUPB relatively later.Accordingly, the level tracing voltage generation unit 200B controls thelevel tracing voltage V_LEVEL to have a higher voltage level before thepower-up. After the power-up, the target voltage V_TARGET may be setrelatively low so that a reset of the power-up signal PWRUPB rarelyoccurs. Accordingly, the level tracing voltage generation unit 200Bcontrols the level tracing voltage V_LEVEL to have a lower voltage levelafter the power-up.

The power-up signal generation unit 400 generates the power-up signalPWRUPB based on the level tracing voltage V_LEVEL. A feedback on thepower-up signal PWRUPB generated from the power-up signal generationunit 400 is given to the control signal generation unit 100.

The power-up signal generation unit 400 may include the detectionvoltage generation section 400A and a power-up signal output section400C. The detection voltage generation section 400A generates adetection voltage V_DET with a voltage level controlled in response tothe level tracing voltage V_LEVEL. The power-up signal output section400C outputs the power-up signal PWRUPB based on the detection voltageV_DET.

The detection voltage generation section 400A includes a PMOS transistorP4 and an NMOS transistor N4 coupled between the supply voltage (VDD)terminal and the ground voltage (VSS) terminal in series. The PMOStransistor P4 is coupled between the supply voltage (VDD) terminal and afifth node ND5, and has a gate for receiving the ground voltage VSS.Since the PMOS transistor P4 is turned on by the ground voltage VSSapplied to its gate, an initial voltage level of the fifth node ND5maintains a supply voltage (VDD) level. The NMOS transistor N4 iscoupled between the fifth node ND5 and the ground voltage (VSS)terminal, and has a gate receiving the level tracing voltage V_LEVEL.The detection voltage V_DET is outputted through the fifth node ND5.Since the extent of the turn-on of the NMOS transistor N4 is determinedbased on the level tracing voltage V_LEVEL applied to its gate, thedetection voltage V_DET may have a voltage level controlled by the leveltracing voltage V_LEVEL.

The power-up signal output section 400C may change a logic level of thepower-up signal PWRUPB when the detection voltage V_DET has a levelhigher than a logic threshold value of an inverter INV10. The power-upsignal output section 400C may include the inverter INV10 and aninverter INV11, which are connected in series, to output the power-upsignal PWRUPB.

FIG. 9 is a detailed diagram of the control signal generation unit 100shown in FIG. 8.

Referring to FIG. 9, the control signal generation unit 100 may includea first edge-triggered flip-flop 910A, a second edge-triggered flip-flop910B and an initialization section 920.

The first and second edge-triggered flip-flops 910A and 910B generatethe first and second control voltages VCTRL1 and VCTRL2, respectively,in response to the power-up signal PWRUPB. The first and secondedge-triggered flip-flops 910A and 910B are disabled before thepower-up, and invert and output the voltage levels of the first andsecond control voltages VCTRL1 and VCTRL2, respectively, whenever thepower-up signal PWRUPB toggles to a logic low level from a logic highlevel.

The first edge-triggered flip-flop 910A may include afalling-edge-triggered flip-flop which inverts and outputs the voltagelevel of the first control voltage VCTRL1 at its output terminal Qwhenever the power-up signal PWRUPB toggles to a logic low level from alogic high level. That is, the ground voltage VSS is inputted to thefirst edge-triggered flip-flop 910A through its data input terminal D,and the power-up signal PWRUPB is inputted to the first edge-triggeredflip-flop 910A through its clock terminal CLK. The second edge-triggeredflip-flop 910B may include a falling-edge-triggered flip-flop whichinverts and outputs the voltage level of the second control voltageVCTRL2 at its output terminal Q whenever the power-up signal PWRUPBtoggles from a logic high level to a logic low level. That is, thesupply voltage VDD is inputted to the second edge-triggered flip-flop910B through its data input terminal D, and the power-up signal PWRUPBis inputted to the second edge-triggered flip-flop 910B through itsclock terminal CLK.

The initialization section 920 initializes the first control voltageVCTRL1 to the supply voltage VDD and the second control voltage VCTRL2to the ground voltage VSS when the power-up signal PWRUPB is in adeactivated state, that is, before the power-up. The initializationsection 920 may include an NMOS transistor N5 and a PMOS transistor P5.The PMOS transistor P5 is coupled between the supply voltage (VDD)terminal and the output node of the first edge-triggered flip-flop 910A,and has a gate receiving the power-up signal PWRUPB inverted. The NMOStransistor N5 is coupled between the output node of the secondedge-triggered flip-flop 910B and the ground voltage (VSS) terminal, andhas a gate for receiving an inverted signal of the power-up signalPWRUPB through an inverter IV2.

Accordingly, the PMOS transistor P5 and the NMOS transistor N5 of theinitialization section 920 are turned on to initialize the first controlvoltage VCTRL1 to the supply voltage VDD and the second control voltageVCTRL2 to the ground voltage VSS before the power-up, respectively. ThePMOS transistor P5 and the NMOS transistor N5 are turned off after thepower-up.

Hereinafter, an operation of the power-up signal generation circuit ofFIG. 8 will be described with reference to FIGS. 8 to 11.

FIG. 10 is a table showing parameters for describing an operation of thepower-up signal generation circuit shown in FIG. 8, such as VCTRL1,VCTRL2, R1, R2, V_LEVEL and V_TARGET. FIG. 11 is a waveform diagramshowing voltages varying before and after the power-up in the power-upsignal generation circuit shown in FIG. 8.

Referring to FIGS. 8 and 10, before the power-up, the resistance of thefirst variable resistor R1 is controlled to have a minimum value[R1(min)−{R1(delta)*VDD}] in response to the first control voltageVCTRL1 having a supply voltage (VDD) level, and the resistance of thesecond variable resistor R2 is controlled to have a value R2(min)greater than the resistance of the first variable resistor R1, inresponse to the second control voltage VCTRL2 having a ground voltage(VSS) level.

As the resistance of the second variable resistor R2 is greater than theresistance of the first variable resistor R1 before the power-up, thelevel tracing voltage V_LEVEL at the fourth node ND4 becomes higher.Since the NMOS transistor N4 is strongly turned on in response to thelevel tracing voltage V_LEVEL becoming higher, the voltage level of thedetection voltage V_DET at the fifth node ND5 becomes lower.Accordingly, the power-up signal PWRUPB is deactivated to a logic highlevel in response to the voltage level of the detection voltage V_DETbecoming lower.

That is, referring to FIG. 11, before the power-up, the level tracingvoltage V_LEVEL having a higher voltage level is outputted at the fourthnode ND4 so that the power-up signal PWRUPB is activated to a logic lowlevel after the supply voltage VDD becomes higher than the targetvoltage V_TARGET. Accordingly, the power-up timing when the supplyvoltage VDD reaches the voltage level of the target voltage V_TARGET maybe adjusted.

After the power-up, the resistance of the first variable resistor R1 iscontrolled to have a minimum value R1(min) in response to the firstcontrol voltage VCTRL1 having the ground voltage (VSS) level, and theresistance of the second variable resistor R2 is controlled to have avalue [R2(min)−{R2(delta)*VDD}] smaller than the resistance of the firstvariable resistor R1, in response to the second control voltage VCTRL2having the supply voltage (VDD) level.

As the resistance of the second variable resistor R2 is smaller than theresistance of the first variable resistor R1 after the power-up, thelevel tracing voltage V_LEVEL at the fourth node ND4 becomes lower.Since the NMOS transistor N4 is weakly turned on in response to thelevel tracing voltage V_LEVEL becoming lower, the voltage level of thedetection voltage V_DET at the fifth node ND5 becomes higher.Accordingly, the power-up signal PWRUPB is activated to a logic lowlevel in response to the voltage level of the detection voltage V_DETbecoming higher.

That is, referring to FIG. 11, after the power-up, the level tracingvoltage V_LEVEL having a lower voltage level is outputted through thefourth node ND4 to control the target voltage V_TARGET to be lower sothat a reset of the power-up signal PWRUPB rarely occurs.

According to the embodiments of the present invention as describedabove, the power-up signal generation unit may generate a power-upsignal when a voltage level of an external power voltage sufficientlyrises by adjusting a level tracing voltage and increasing a voltagelevel of a target voltage before a power-up. Accordingly, thereliability on an overall operation of a semiconductor device may beimproved.

Furthermore, according to the embodiments of the present invention asdescribed above, the power-up signal generation unit may prevent aninadvertent reset of an operating semiconductor device by adjusting alevel tracing voltage and decreasing a voltage level of a target voltageafter a power-up.

While the present invention has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

For instance, positions and kinds of the logic gates and transistorsexemplified in the above-described embodiment should be differentlyimplemented according to the polarities of the signals input thereto.

What is claimed is:
 1. A power-up signal generation circuit comprising:a control signal generation unit suitable for generating first andsecond control voltages based on a power-up signal; a level tracingvoltage generation unit suitable for generating a level tracing voltagewith a voltage level that varies based on the first and second controlvoltages; and a power-up signal generation unit suitable for generatingthe power-up signal based on the level tracing voltage, and providingfeedback on the power-up signal to the control signal generation unit,wherein the first control voltage is initialized to a first voltage andthe second control voltage is initialized to a second voltage before thepower-up signal is activated, and wherein the voltage levels of thefirst and second control voltages are inverted, respectively, wheneverthe power-up signal toggles after the power-up signal is activated. 2.The power-up signal generation circuit of claim 1, wherein the leveltracing voltage generation unit comprises: first and second variableresistors coupled in series between a supply voltage terminal and aground voltage terminal, wherein the level tracing voltage is outputtedfrom a first node between the first and second variable resistors. 3.The power-up signal generation circuit of claim 2, wherein a resistanceof the first variable resistor is inversely proportional to a voltagelevel of the first control voltage, and a resistance of the secondvariable resistor is inversely proportional to a voltage level of thesecond control voltage.
 4. The power-up signal generation circuit ofclaim 3, wherein, before the power-up signal is activated, the controlsignal generation unit generates the first control voltage such that theresistance of the first variable resistor is set to a minimum value, andgenerates the second control voltage such that the resistance of thesecond variable resistor becomes gradually lower than the resistance ofthe first variable resistor.
 5. The power-up signal generation circuitof claim 3, wherein, after the power-up signal is activated, the controlsignal generation unit generates the second control voltage such thatthe resistance of the second variable resistor is set to a minimumvalue, and generates the first control voltage such that the resistanceof the first variable resistor becomes gradually lower than theresistance of the second variable resistor.
 6. The power-up signalgeneration circuit of claim 1, wherein the power-up signal generationunit comprises: a detection voltage generation section suitable forgenerating a detection voltage based on the level tracing voltage; and apower-up signal output section suitable for outputting the power-upsignal by inverting the detection voltage.
 7. The power-up signalgeneration circuit of claim 6, wherein the detection voltage generationsection comprises a PMOS transistor and a NMOS transistor coupled inseries between a supply voltage terminal and a ground voltage terminal,wherein the detection voltage is outputted from a second node betweenthe PMOS transistor and the NMOS transistor.
 8. The power-up signalgeneration circuit of claim 7, wherein the PMOS transistor maintains avoltage of the second node at a supply voltage level, and the NMOStransistor is turned on based on the level tracing voltage and adjuststhe voltage of the second node to have a value between the supplyvoltage level and a ground voltage level.
 9. The power-up signalgeneration circuit of claim 1, wherein the control signal generationunit generates the first control voltage having a ground voltage leveland generates the second control voltage having a supply voltage levelbefore the power-up signal is activated; and the control signalgeneration unit inverts and outputs voltage levels of the first andsecond control voltages when the power-up signal toggles after thepower-up signal is activated.
 10. The power-up signal generation circuitof claim 9, wherein the control signal generation unit includes: a firstrising edge-triggered flip-flop suitable for receiving a ground voltageat its data input terminal and the power-up signal at its clockterminal, and outputting the first control voltage at its outputterminal; a second rising edge-triggered flip-flop suitable forreceiving a supply voltage at its data input terminal and the power-upsignal at its clock terminal, and outputting the second control voltageat its output terminal; and an initialization section suitable forinitializing the first control voltage to the ground voltage and thesecond control voltage to the supply voltage before the power-up signalis activated.
 11. The power-up signal generation circuit of claim 2,wherein a resistance of the first variable resistor is inverselyproportional to a voltage level of the first control voltage, and aresistance of the second variable resistor is inversely proportional toa voltage level of the second control voltage.
 12. The power-up signalgeneration circuit of claim 11, wherein, before the power-up signal isactivated, the control signal generation unit generates the secondcontrol voltage such that the resistance of the second variable resistoris set to a minimum value, and generates the first control voltage suchthat the resistance of the first variable resistor gradually becomeslower than the resistance of the second variable resistor.
 13. Thepower-up signal generation circuit of claim 11, wherein, after thepower-up signal is activated, the control signal generation unitgenerates the first control voltage such that the resistance of thefirst variable resistor is set to a minimum value, and generates thesecond control voltage such that the resistance of the second variableresistor gradually becomes lower than the resistance of the firstvariable resistor.
 14. The power-up signal generation circuit of claim1, when the power-up signal is activated, the voltage level of the leveltracing voltage is higher than before the power-up signal is activated.15. A power-up signal generation circuit comprising: a control signalgeneration unit suitable for generating first and second controlvoltages based on a power-up signal; a level tracing voltage generationunit suitable for generating a level tracing voltage with a voltagelevel that varies based on the first and second control voltages,wherein, when the power-up signal is activated, the voltage level of thelevel tracing voltage is higher than before the power-up signal isactivated; and a power-up signal generation unit suitable for generatingthe power-up signal based on the level tracing voltage, and providingfeedback on the power-up signal to the control signal generation unit,wherein the level tracing voltage generation unit comprises first andsecond variable resistors and a compensation unit coupled in seriesbetween a supply voltage terminal and a ground voltage terminal, andwherein the compensation unit is enabled based on a voltage level of athird node between the first and second variable resistors, and thelevel tracing voltage is outputted from a fourth node between the secondvariable resistor and the compensation unit.
 16. A power-up signalgeneration circuit comprising: a control signal generation unit suitablefor generating first and second control voltages based on a power-upsignal; a level tracing voltage generation unit suitable for generatinga level tracing voltage with a voltage level that varies based on thefirst and second control voltages, wherein, when the power-up signal isactivated, the voltage level of the level tracing voltage is higher thanbefore the power-up signal is activated; and a power-up signalgeneration unit suitable for generating the power-up signal based on thelevel tracing voltage, and providing feedback on the power-up signal tothe control signal generation unit, wherein the control signalgeneration unit generates the first control voltage having a supplyvoltage level and generates the second control voltage having a groundvoltage level before the power-up signal is activated, and the controlsignal generation unit inverts and outputs voltage levels of the firstand second control voltages when the power-up signal toggles after thepower-up signal is activated, wherein the control signal generation unitincludes: a first falling edge-triggered flip-flop suitable forreceiving a ground voltage at its data input terminal and the power-upsignal at its clock terminal, and outputting the first control voltageat its output terminal; a second falling edge-triggered flip-flopsuitable for receiving a supply voltage at its data input terminal andthe power-up signal at its clock terminal, and outputting the secondcontrol voltage at its output terminal; and an initialization sectionsuitable for initializing the first control voltage to the groundvoltage and the second control voltage to the supply voltage before thepower-up signal is activated.